This invention relates to secure configuration of a field configurable logic device.
Field configurable devices, such as field programmable gate arrays (FPGAs), are typically configured using data that is supplied to the device after the device is deployed in an application. For example, the configuration data is provided to the device when the device is powered on.
It may be desirable to avoid disclosure of the configuration data. For example, the configuration data may include secrets, such as cryptographic keys or procedures, that are necessary to keep private. It may be also desirable to prevent configuration of the device with unauthorized configuration data.
Referring to FIG. 1, one approach that has been used to provide security for an FPGA 110 is to implement a decryptor function 140 (e.g., a 3DES decryptor) and a volatile memory function 120 (e.g., static RAM) on the same devices as the configurable logic 150. The volatile memory holds a cryptographic key 125 that is provided to the decryptor function. Configuration data 160 for the device is provided to the device in an encrypted form 180 and a configuration module 145 uses the decryptor 140 to decrypt the configuration data as it is loaded into the device before it is used to configure the configurable logic. The cryptographic keys are set and stored on the device before it is deployed, and a dedicated battery 130 is used to maintain the volatile memory—if the battery is removed then the keys are erased. The provider of the configuration data knows the keys stored in the device and therefore can encrypt (170) the configuration data suitably for a particular device. An example of this approach is type of approach is commercially available in the Xilinx Virtex II™ family of FPGAs.
Authentication of integrated circuits has been suggested using device characteristics that vary from device to device based on variation in the fabrication process. Some such approaches are described in US Application Publication US2003/0204743A1, titled “Authentication of Integrated Circuits,” which is incorporated herein by reference.